Generally, a vehicle tracking system comprises a central control station CCS, a plurality of base stations Sl-Sn, and equipment mounted on a vehicle as shown in FIG. 1. When a user requests the central control station CCS to inform him of a position of a vehicle, the central control station CCS transmits a call signal, including an identification number of the vehicle, through a call antenna. The equipment mounted on the vehicle transmits a signal showing its position to the central control station CCS after receiving the call signal including its identification number, and the central control station CCS informs the user of the position of the vehicle by determining the position after receiving the signal. The operation as described in the above statement is performed by a time sharing method as shown in FIG. 2, and every frame is allocated with an address of a vehicle subscriber. The equipment mounted on the vehicle shows its position when a predetermined time has elapsed after receiving a call signal. Because a transmission time is predetermined, the central control station CCS receives a transmission signal from the equipment mounted on the vehicle during a predetermined time for the vehicle. An emergency signal for notifying of an emergency situation of a vehicle is to be transmitted from a frame No. "1" as shown in FIG. 2.
Every frame of a plurality of vehicle subscribers is allocated with its exclusive address. The central control station CCS calls a series of addresses sequentially and receives a signal of position corresponding to a called address sequentially after a predetermined time has elapsed. Accordingly, if trouble occurs on the equipment mounted on the vehicle, the vehicle tracking system is not usable because the transmission time for a position signal is longer than a predetermined time.